1. Field of the Invention
The present invention relates to a thermal recording apparatus and, more particularly, to a recording apparatus for controlling to vary an energy to be applied to heat generating elements in consideration of an ambient temperature of the heat generating elements.
2. Related Background Art
Conventionally, a recording apparatus for performing line-recording of a dot array for one line using a recording head in which heat generating elements are linearly arranged is known. A heat generating temperature of the heat generating elements are influenced by an ambient temperature, and varies depending on whether the adjacent heat generating element generates heat or not. Therefore, in a conventional recording apparatus of this type, an energy applied to the heat generating elements, more specifically, an applying time of a voltage, is varied so that the temperature of the heat generating elements for performing recording is kept constant. A sequence for setting an applying time of a voltage will be described below with reference to FIG. 6.
FIG. 6 shows the positional relationship between a dot position of an object to be recorded, and dot data used for setting a voltage applying time.
An applying time of a dot 50 to be recorded is determined using dot data at positions a to g in FIG. 6. That is, if dot data (black data indicating the presence of dot recording is represented by "1", and blank data indicating the absence of dot recording is represented by "0") are represented by A to G in correspondence with positions a to g, a pulse applying time is determined by: ##EQU1##
A maximum pulse width of one dot corresponds to a numeric value obtained by multiplying a maximum electricity supply time assigned to each divided block of the heat generating elements by coefficients 0 to 1 according to thermistor temperature data.
For example, in order to allow line-recording of an A4-sized recording member, the number of heat generating elements for one line is set to be 1728, the heat generating element group is divided into four blocks, and a recording time for one line is set to be 2.5 ms. A maximum allowable electricity supply time for applying a voltage of 24 V to all the 432 elements in one block is given by 2.5 ms.div.4=0.625 ms. The temperature of the heat generating elements is kept constant, thus allowing high-quality dot recording.
However, as the recording speed and recording pixel density become higher, dot image quality tends to be degraded. This problem remains unsolved.
As applications associated with heat hysteresis control, U.S. Pat. Nos. 4,737,860 and 4,875,056 are known. However, no applications which can solve the above problem have not yet been proposed.